This invention relates to a polyphenylene ether thermoplastic resin composition which is excellent in impact resistance, particularly surface impact strength.
Polyphenylene ether resin is one of the engineering plastics having excellent properties such as heat resistance, mechanical properties and the like.
Said polyphenylene ether resins have already been disclosed in prior art references, for example, U.S. Pat. Nos. 3,306,874; 3,306,875 and 3,573,257, etc.
Polyphenylene ether resins have such disadvantages that their moldability is poor and their impact resistance is low though they have excellent properties as mentioned above. In order to overcome such disadvantages, various methods have been proposed. For making moldability better, there is known a method comprising blending with the polyphenylene ether resin a styrene homopolymer which is compatible with the polyphenylene ether resin, and for improving the impact resistance, there is known a method comprising blending and dispersing a rubber therein. In particular, the rubber-modified styrene copolymers are effective in that moldability and impact resistance can be simultaneously improved. Particularly, polybutadiene rubber on which styrene has been graft-copolymerized (referred to hereinafter as BR-HIPS) is generally used. For example, U.S. Pat No. 3,383,435 discloses polyphenylene ether resin/BR-HIPS.
In particular, in order to improve impact resistance, for example, JP-B-47-32,731 discloses blending a polybutadiene rubber with a polyphenylene ether resin. This is also disclosed in JP-A-46-2,345, JP-A-48-74,552, JP-A-49-85,144, U.S. Pat Nos. 3,835,200 and 3,994,856.
However, polybutadiene (referred to hereinafter as BR) has unsaturations in the polymer main chain, and hence, is instable against heat and light. As a result, when a polybutadiene rubber is blended with a polyphenylene ether resin, the heat stability, light stability and weather resistance of the resulting resin composition are unsatisfactory in practice.
Moreover, U.S. Pat. No. 3,361,851 and JP-B-42-7,069 propose blending a polyolefin with a polyphenylene ether resin to improve the moldability of the polyphenylene ether resin and also improve the impact resistance of a molded article obtained therefrom. Polyolefin is superior to BR in heat stability and light stability. However, polyolefin is essentially inferior in compatibility with the polyphenylene ether resin, and hence, for example, when at least 5% by weight of a polyolefin is blended with the polyphenylene ether resin, phase separation is clearly observed in the resin composition obtained. When the amount of polyolefin blended exceeds 10% by weight, delamination is caused. Accordingly, when a polyolefin is merely simply blended with the polyphenylene ether resin, the appearance of the molded article obtained is inferior and the impact resistance thereof is not improved.
JP-A-49-75,663 discloses blending, with a polyphenylene ether resin, a polyolefin graft-copolymerized with styrene for improving its compatibility with the polyphenylene ether resin, to improve the moldability of the resulting resin composition while retaining the practical mechanical strength of the polyphenylene ether resin. The polyolefin disclosed therein is substantially crystalline.
As another proposal for improving the impact resistance of a polyphenylene ether resin, for example, U.S. Pat No. 3,920,770 discloses a composition in which a substantially non-crystalline ethylene-propylene-non-conjugated diene copolymer rubber (referred to hereinafter as EPDM) is blended as a kind of polyolefin with the polyphenylene ether resin. With EPDM alone, its compatibility with the polyphenylene ether resin is insufficient, phase separation is caused and the impact strength is also insufficient, so that it cannot be used in practice.
Many proposals have been made according to which styrene is graft-copolymerized on EPDM for improving the compatibility of EPDM, and the thus graft-copolymerized EPDM (referred to hereinafter as EPDM-HIPS) is blended with a polyphenylene ether resin to obtain a composition excellent in impact resistance, heat stability, light stability and weather resistance. For example, JP-B-47-43,174, JP-B-47-43,290, U.S. Pat Nos. 3,943,192, 3,959,211, 3,974,235, 4,127,588 4,152,316, 4,101,505, 4,101,503, 4,101,504 and JP-A-58-111,854 disclose the above proposals.
For the purpose of further improving the impact resistance, a composition comprising EPDM-HIPS and other impact-resistance-improving agents has been proposed. As said other impact-resistance-improving agents, for example, U.S. Pat. Nos. 3,981,841 and 4,020,124 disclose EPDM-HIPS prepared by an emulsion polymerization method and BR graft-copolymerized with methyl methacrylate alone or along with styrene and styrene-butadiene copolymer, both being prepared by an emulsion polymerization method; U.S. Pat. Nos. 4,143,095, 4,172,826 and 4,172,929 disclose a hydrogenated styrene-butadiene-styrene triblock copolymer rubber; U.S. Pat. No. 4,139,574 discloses a hydrogenated styrene-butadiene radial teleblock copolymer; U.S. Pat. No. 4,196,116 discloses a hydrogenated styrene-butadiene diblock copolymer rubber or a hydrogenated isoprene diblock copolymer rubber; U.S. Pat. No. 4,311,633 discloses a styrene-butyl acrylate copolymer; JP-B-63-4,590, JP-A-1-56,100 and JP-A-4-33,306 disclose BR-HIPS; U.S. Pat. No. 4,365,038 discloses a silicone oil; JP-B-63-4,589 discloses a poly-.alpha.-olefin; and U.S. Pat. No. 4,373,045 discloses an ethylene-propylene copolymer rubber (referred to hereinafter as EPM).
Moreover, many proposals have been made as to compositions having excellent impact resistance, heat stability, light stability and weather resistance prepared by blending, with a polyphenylene ether resin, a styrene-grafted ethylene-.alpha.-olefin copolymer rubber (referred to hereinafter as EPM-HIPS) along with other impact-resistance-improving agents. For example, as said other impact-resistance-improving agents, JP-A-57-139,140 and JP-A-60-36,550 disclose BR-HIPS; and JP-A-59-140,257 discloses a hydrogenated styrene-butadiene-styrene triblock copolymer and a combination system thereof with BR-HIPS.
Also, a composition having excellent impact resistance, heat stability, light stability and weather resistance prepared by blending EPDM-HIPS with a styrene-grafted polyphenylene ether resin has been proposed (see, for example, JP-B-53-39,698 and JP-B-55-44,026).
JP-A-60-36,551 discloses a composition having improved impact resistance and mold release characteristics prepared by blending, with a polyphenylene ether resin, EPDM grafted with styrene and acrylonitrile, BR-HIPS, a styrene-butadiene-styrene triblock copolymer and EPM.
Furthermore, U.S. Pat. No. 4,365,042 discloses a composition having excellent room-temperature impact strength and low-temperature impact strength prepared by blending a silicone rubber grafted EPDM with a polyphenylene ether resin.
Resins are used in automotive parts such as bumper, wheel cover, instrument panel, console box, internal trim parts for door such as pillar/trim and the like. Also, flame retardant resins are used in parts of office automation equipment such as housing and the like. With respect to the automotive parts and parts of office automation equipment, they are required to be resistant to each of light, heat and water and even to a complex influence of them, that is, resistant to weather. Also, these parts are required to have so high level impact resistance at room temperature or low temperatures, particularly surface impact strength that they withstand the collision of other objects or the impact caused by the falling of finished goods having built therein these parts.
Compositions prepared by blending the heretofore proposed EPDM-HIPS or EPM-HIPS or a combination thereof with other impact modifiers with a polyphenylene ether resin have such a problem that they do not satisfy particularly the surface impact strength among the above required characteristics.
As explained above, notwithstanding that many proposals have been made by now for improving the impact resistance of a polyphenylene ether resin, none of the compositions proposed have exhibited satisfactory surface impact strength.